In the mining technology, compared to the underground mining method, the generally adopted open-pit mining method at present has the advantages of full resource utilization, low cost, high recovery rate, fast construction of mines, high output, a better working condition, and a safer working environment. However, the open-pit mining method has the disadvantages of being severely limited by natural occurrence conditions. In addition, during the course of mining, large area of fertile farmlands are occupied, and noticeable anthropogenic changes occur to the ecological environment of the mining region, which are manifested in destructions to the landform, heavy metal pollution, and aggravated water loss and soil erosion. Furthermore, due to the fact that open-pit mines are mostly located at the ecologically fragile arid/semi-arid regions, the functional life support system of the open-pit mining region is lost, in particular, the vegetation system is damaged, thereby further increasing the vulnerability of the ecological environments and the degeneration rate, as well as threatening severely the ecological safety of the mining region.
Although the underground mining method is more environment-friendly, the increased mining difficulty and the more hostile environment of the underground mining method compared with the open-pit mining method raises a higher requirement for the mining equipment, the operator qualification, and the mining process. For example, in some mining regions, permanent frozen earth with thickness of 50 to 98 m and comprising quaternary humus soils, sandy soils, partial bed rocks and the like is widely spread and, which likely results in the problem of deteriorated engineering geology, a building cycle of at least 5 years within such mining regions and high investment cost. Therefore, it is hard for enterprises to sustain. Moreover, a main shaft, an auxiliary shaft, and a ventilating shaft are typically required to be dug in the conventional underground mining process, resulting in crisscrossed underground tunnels. As a result, the damaged underground after mining cannot be recovered and the secondary disaster brought by the subsidence of the mined region cannot be avoided. In particular, the grassland landform damaged by the gangue field cannot be restored and the stacked wastes have to be left permanently in the mining region, which is adverse to the recovery of the ecological environment. Additionally, some other secondary disasters, such as gas and coal dust, roof collapse, wall caving, water leakage and the like, may also be induced by the underground mining method.
Therefore, developing an environment-friendly coal mining method that enables cost saving, simple operations and safe production is a challenging problem to be solved.